1. Field
The present invention relates to a display device and a liquid crystal display device including a light source unit using a point light source.
2. Description of the Related Art
In general, a display device includes a display panel, a circuit substrate and a light source unit. The types of the light source unit for irradiating the display panel with light from the rear side of the display panel may include a side light type (also called an edge light type) in which light sources are disposed on the side face of a housing, a direct light type in which light sources are disposed on the bottom surface of a housing to oppose the display panel, etc.
The side light type light source unit may typically include a light guide plate for guiding light from the light sources to an opening of the housing. The light source unit using the light guide plate is configured to draw planar light out of the opening of the housing by propagating light emitted from line light sources such as cold cathode tubes or point light sources such as light emitting diodes (LEDs) into the light guide plate and diffusing the light with a diffusing pattern provided on the bottom and/or top of the light guide plate.
In order to increase brightness of images displayed on a screen of the light source unit using the point light sources such as LEDs, it may be considered to increase the number of point light sources such that the density of the point light sources increases, or to increase current supplied to the point light sources. In either case, the temperature at the circumference of the point light sources becomes high due to heat generated from the point light sources in light emission, which may result in decrease of emission efficiency of the point light sources and reduction of their lifetime.
JP-A-2005-38771 discloses a structure of a display device, which is capable of improving heat-radiation property and exchanging old light sources for new ones if necessary. In the display device disclosed in JP-A-2005-38771, metal with high heat radiation property or ceramics is used for an LED substrate. The LEDs as point light sources are mounted on a mounting surface of the LED substrate. The rear surface of the LED substrate, which is opposite to the mounting surface, is closely attached to the inner side face of an LED cover, and the LED cover is fitted into a display plate case for accommodating a display plate. According to this configuration, heat generated due to lighting of the LEDs is radiated as the heat is transferred from the LED substrate to the display plate case via the LED cover and a fit portion. In addition, a portion of the LED cover is exposed to the outside and thus is cooled by external air. If exhausted LEDs are to be exchanged for new ones, the LED substrate is detached and separated from the LED cover.
JP-A-2002-107721 discloses a liquid crystal display module in which a light source substrate is fixed by disposing the light source substrate to be brought into contact with a substrate support part formed at a case, and then fixing a light guide plate to the case. In this disclosed liquid crystal display module, since the light source substrate is fixed without using screws or an adhesive, it is possible to easily separate the light source substrate from the case by separating the light guide plate from the case.
However, the display device and the liquid crystal display module disclosed in JP-A-2005-38771 and JP-A-2002-107721 have a problem of reliability since they do not have a structure which is capable of sufficiently radiating heat generated from the light sources. In addition, the device or the module is necessarily disassembled for separation of the light source substrate. Particularly, after the display device or the module is mounted on electronic equipments, the operation for exchanging the light sources is complicated.